Method and apparatus for encoding and decoding image

Abstract

An image encoding apparatus includes a multidirectional predicting unit configured to predict a plurality of pixel blocks by using an encoded pixel as a reference pixel according to a plurality of prediction modes having different prediction directions to generate a plurality of first prediction signals corresponding to the pixel blocks obtained by dividing a frame of an input image signal a setting unit configured to set a weighting factor depending on the prediction directions of the plurality of prediction modes and a spatial distance between a prediction pixel in the pixel block and the reference pixel, a weighted average unit configured to calculate a weighted average of the plurality of first prediction signals according to the weighting factor to generate one second prediction signal corresponding to the pixel blocks, and an encoding unit configured to encode a prediction residual error signal representing a difference between an image signal of the pixel block and at least the second prediction signal to generate encoded data.

1 . An image encoding method comprising:
 predicting a plurality of pixel blocks by using an encoded pixel as a reference pixel according to a plurality of prediction modes having different prediction directions to generate a plurality of first prediction signals corresponding to the pixel blocks obtained by dividing a frame of an input image signal;   setting a weighting factor depending on the prediction directions of the plurality of prediction modes and a spatial distance between a prediction pixel in the pixel block and the reference pixel;   calculating a weighted average of the plurality of prediction signals according to the weighting factor to generate one second prediction signal corresponding to the pixel block; and   encoding a prediction residual error signal representing a difference between an image signal of the pixel block and the second prediction signal to generate encoded data.   
     
     
         2 . An image encoding apparatus comprising:
 a multidirectional predicting unit configured to predict a plurality of pixel blocks by using an encoded pixel as a reference pixel according to a plurality of prediction modes having different prediction directions to generate a plurality of first prediction signals corresponding to the pixel blocks obtained by dividing a frame of an input image signal;   a setting unit configured to set a weighting factor depending on the prediction directions of the plurality of prediction modes and a spatial distance between a prediction pixel in the pixel block and the reference pixel;   a weighted average unit configured to calculate a weighted average of the plurality of first prediction signals according to the weighting factor to generate one second prediction signal corresponding to the pixel block; and   an encoding unit configured to encode a prediction residual error signal representing a difference between an image signal of the pixel block and at least the second prediction signal to generate encoded data.   
     
     
         3 . The image encoding apparatus according to  claim 2 , wherein
 at least one of the plurality of prediction modes is an intra-frame prediction mode.   
     
     
         4 . The image encoding apparatus according to  claim 2 , further comprising:
 a unidirectional predicting unit configured to predict the pixel block by using an encoded pixel as a reference pixel according to a single prediction mode to generate one third prediction signal corresponding to each of the pixel blocks;   a selecting unit configured to select any one of the second prediction signal and the third prediction signal; and   a subtracting unit configured to calculate a difference between the image signal of the pixel block and the second prediction signal to generate the prediction residual error signal when the second prediction signal is selected and calculate a difference between the image signal of the pixel block and the third prediction signal to generate the prediction residual error signal when the third prediction signal is selected.   
     
     
         5 . The image encoding apparatus according to  claim 2 , wherein
 the selecting unit is configured to select any one of the second prediction signal and the third prediction signal according to a prediction mode count selected from a plurality of prediction mode counts, and   the encoding unit is configured to also encode information representing the selected prediction mode count to generate the encoded data.   
     
     
         6 . The image encoding apparatus according to  claim 2 , wherein
 the setting unit is configured to set the weighting factor by calculating the weighting factor depending on the prediction directions and the spatial distance.   
     
     
         7 . The image encoding apparatus according to  claim 2 , wherein
 the setting unit is configured to calculate a sum of reliabilities based on the spatial distances of the plurality of prediction modes as a denominator and calculate the reliability as a numerator to set the weighting factor.   
     
     
         8 . The image encoding apparatus according to  claim 7 , wherein
 the reliability is configured to be monotonously decreased depending on the spatial distance.   
     
     
         9 . The image encoding apparatus according to  claim 7 , wherein
 the reliability is configured to conform to at least one of (a) an auto-correlation function model including an isotropic correlation model and an elliptic correlation model, (b) a proportion/inverse proportion model, (c) an N-order function (N≧1) model, (d) a generalized Gaussian distribution model, and (e) a table in which weighting factors depending on the number of prediction modes are described, depending on the prediction direction and the spatial distance.   
     
     
         10 . The image encoding apparatus according to  claim 7 , wherein the setting unit is configured to calculate, with respect to a plurality of distance components obtained by separating the spatial distance, reliability components of the distance components according to evaluation rules of the distance components and to calculate the reliability from the reliability components. 
     
     
         11 . The image encoding apparatus according to  claim 7 , wherein
 the setting unit is configured to calculate, with respect to a horizontal distance component and a vertical distance component obtained by separating the spatial distance, reliability components of the distance components according to evaluation rules of the distance components and to calculate the reliability from the reliability components.   
     
     
         12 . The image encoding apparatus according to  claim 2 , wherein
 the setting unit prepares a plurality of sets of the weighting factors in units of at least one of sequences, pictures, slices, macro-blocks, and sub-blocks, and   the weighted average unit is configured to selectively use the sets of the weighting factors.   
     
     
         13 . The image encoding apparatus according to  claim 12 , wherein
 the encoding unit is configured to also encode information representing the set of the weighting factors used by the weighted average unit to generate the encoded data.   
     
     
         14 . The image encoding apparatus according to  claim 12 , wherein
 the weighted average unit is configured to select the set of the weighting factors depending on activity information including at least one of a correlation and a variance of pixels in an encoded adjacent block.   
     
     
         15 . The image encoding apparatus according to  claim 6  or  7 , wherein
 the setting unit prepares a plurality of sets of the reliabilities in units of at least one of sequences, pictures, slices, macro-blocks, and sub-blocks, and   the weighted average unit is configured to selectively use the sets of the reliabilities.   
     
     
         16 . The image encoding apparatus according to  claim 15 , wherein
 the encoding unit is configured to also encode information representing the set of the reliabilities used by the weighted average unit to generate the encoded data.   
     
     
         17 . The image encoding apparatus according to  claim 15 , wherein
 the weighted average unit is configured to select the set of the reliabilities depending on activity information including at least one of a correlation and a variance of pixels in an encoded adjacent block.   
     
     
         18 . An image decoding method comprising:
 decoding encoded data including the prediction residual error signals to generate prediction residual error signals corresponding to a plurality of pixel blocks obtained by dividing a frame of an image signal;   predicting the pixel blocks by using a decoded pixel as a reference pixel according to a plurality of prediction modes having different prediction directions to generate a plurality of first prediction signals corresponding to the pixel blocks;   setting a weighting factor depending on the prediction directions of the plurality of prediction modes and a spatial distance between a prediction pixel in the pixel block and the reference pixel;   calculating a weighted average of the plurality of first prediction signals according to the weighting factor to generate one second prediction signal corresponding to the pixel block; and   generating the prediction residual error signal and a decoding image signal by using at least the second prediction signal.   
     
     
         19 . An image decoding apparatus comprising:
 a decoding unit configured to decode encoded data including the prediction residual error signals to generate prediction residual error signals corresponding to a plurality of pixel blocks obtained by dividing a frame of an image signal;   a multidirectional predicting unit configured to predict the pixel blocks by using a decoded pixel as a reference pixel according to a plurality of prediction modes having different prediction directions to generate a plurality of first prediction signals corresponding to the pixel blocks;   a setting unit configured to set a weighting factor depending on the prediction directions of the plurality of prediction modes and a spatial distance between a prediction pixel in the pixel block and the reference pixel;   a weighted average unit configured to calculate a weighted average of the plurality of first prediction signals according to the weighting factor to generate one second prediction signal corresponding to the pixel block; and   a generating unit configured to generate the prediction residual error signal and a decoding image signal by using at least the second prediction signal.   
     
     
         20 . The image decoding apparatus according to  claim 19 , wherein
 at least one of the plurality of prediction modes is an intra-frame prediction mode.   
     
     
         21 . The image decoding apparatus according to  claim 19 , further comprising:
 a unidirectional predicting unit configured to predict the pixel block by using a decoded pixel as a reference pixel according to a single prediction mode to generate one third prediction signal corresponding to each of the pixel blocks; and   a selecting unit which selects any one of the second prediction signal and the third prediction signal,   wherein the decoding unit is configured to generate the decoding image signal by using the prediction residual error signal and the second prediction signal when the second prediction signal is selected and generate the decoding image signal by using the prediction residual error signal and the third prediction signal when the third prediction signal is selected.   
     
     
         22 . The image decoding apparatus according to  claim 21 , wherein
 the selecting unit is configured to select any one of the second prediction signal and the third prediction signal according to a prediction mode count selected from a plurality of prediction mode counts; and   the decoding unit is configured to decode the encoded data to generate information representing the selected prediction mode count.   
     
     
         23 . The image decoding apparatus according to  claim 19 , wherein
 the setting unit is configured to set the weighting factor by calculating the weighting factor depending on the prediction directions and the spatial distance.   
     
     
         24 . The image decoding apparatus according to  claim 19 , wherein
 the setting unit is configured to calculate a sum of reliabilities based on the spatial distances of the plurality of prediction modes as a denominator and calculate the reliability as a numerator to set the weighting factor.   
     
     
         25 . The image decoding apparatus according to  claim 24 , wherein
 the reliability is configured to be monotonously decreased depending on the spatial distance.   
     
     
         26 . The image decoding apparatus according to  claim 24 , wherein
 the reliability is configured to conform to at least one of (a) an auto-correlation function model including an isotropic correlation model and an elliptic correlation model, (b) a proportion/inverse proportion model, (c) an N-order function (N≧1) model, (d) a generalized Gaussian distribution model, and (e) a table in which weighting factors depending on the number of prediction modes are described, depending on the prediction direction and the spatial distance.   
     
     
         27 . The image decoding apparatus according to  claim 19 , wherein
 the setting unit prepares a plurality of sets of the weighting factors in units of at least one of sequences, pictures, slices, macro-blocks, and sub-blocks, and   the weighted average unit is configured to selectively use the sets of the weighting factors by the weighted average unit.   
     
     
         28 . The image decoding apparatus according to  claim 27 , wherein
 the encoded data includes information representing a set of the weighting factors used by the weighted average unit to further generate the decoding image signal, and   the decoding unit is configured to decode the encoded data to generate the information representing the set of the weighting factors.   
     
     
         29 . The image decoding apparatus according to  claim 27 , wherein
 the weighted average unit is configured to select the set of the weighting factors depending on activity information including at least one of a correlation and a variance of pixels in a decoded adjacent block.   
     
     
         30 . An image encoding method comprising:
 predicting a plurality of pixel blocks according to a plurality of prediction modes to generate prediction signals corresponding to the pixel blocks obtained by dividing a frame of an input image signal;   encoding a prediction residual error signal representing a difference between an image signal of the pixel block and the prediction signal; and   encoding mode indexes representing the plurality of prediction modes in descending order of values.   
     
     
         31 . An image encoding apparatus comprising:
 a predicting unit which, for a plurality of pixel blocks obtained by dividing a frame of an input image signal, predicts the pixel blocks according to a plurality of prediction modes to generate prediction signals corresponding to the pixel blocks; and   an encoding unit which encodes a prediction residual error signal representing a difference between an image signal of the pixel block and the prediction signal and encodes mode indexes representing the plurality of prediction modes in descending order of values.   
     
     
         32 . The image encoding apparatus according to  claim 31 , wherein
 the encoding unit is configured to predict a second prediction mode having a second mode index to be encoded next from a first prediction mode having a first mode index encoded in advance when the mode index is encoded, predict a maximum value of values obtained by the second mode index, and encode the second mode index with a minimum code length required to express the maximum value.   
     
     
         33 . An image encoding method comprising:
 selecting a prediction order of a plurality of sub-blocks obtained by further dividing each of a plurality of pixel blocks obtained by dividing a frame of an input image signal from a plurality of predetermined prediction orders;   selecting one prediction mode set including a first prediction mode and a second prediction mode from a plurality of prediction mode sets predetermined to correspond to the plurality of prediction orders and including a plurality of prediction modes having different prediction directions according to the selected prediction order;   predicting the pixel blocks in units of the sub-blocks according to the first prediction mode to generate a plurality of prediction signals corresponding to the pixel blocks;   predicting the first prediction mode by using the second prediction mode corresponding to an encoded pixel block predicted according to the second prediction mode to generate a reference prediction mode;   setting a weighting factor to the first prediction signal depending on the prediction directions of the plurality of prediction modes and a spatial distance between a prediction pixel in the pixel block and a reference pixel;   calculating a weighted average of the first prediction signals according to the weighting factor to generate one second prediction signal corresponding to the pixel block; and   encoding a prediction residual error signal representing a difference between an image signal of the pixel block and the second prediction signal, information representing the selected prediction order, and mode information representing the first prediction mode generated on the basis of the reference prediction mode.   
     
     
         34 . An image encoding apparatus comprising:
 a first selecting unit configured to select a prediction order of a plurality of sub-blocks obtained by further dividing each of a plurality of encoding target pixel blocks obtained by dividing a frame of an input image signal from a plurality of predetermined prediction orders;   a second selecting unit configured to select one prediction mode set including a first prediction mode and a second prediction mode from a plurality of prediction mode sets predetermined to correspond to the plurality of prediction orders and including a plurality of prediction modes having different prediction directions according to the selected prediction order;   a first predicting unit configured to predict the encoding target pixel blocks in units of the sub-blocks according to the first prediction mode to generate a plurality of prediction signals corresponding to the encoding target pixel blocks;   a second predicting unit configured to predict the first prediction mode by using the second prediction mode corresponding to an encoded pixel block predicted according to the second prediction mode to generate a reference prediction mode;   a setting unit configured to set a weighting factor to the first prediction signal depending on the prediction directions of the plurality of prediction modes and a spatial distance between a prediction pixel in the encoding target pixel block and a reference pixel;   a weighted average unit configured to calculate a weighted average according to the weighting factor to generate one second prediction signal corresponding to the encoding target pixel block; and   an encoding unit configured to encode a prediction residual error signal representing a difference between an image signal of the encoding target pixel block and the second prediction signal, information representing the selected prediction order, and mode information representing the first prediction mode generated on the basis of the reference prediction mode.   
     
     
         35 . The image encoding apparatus according to  claim 34 , wherein
 the mode information includes a flag representing whether the first prediction mode and the reference prediction mode are matched with each other and further includes a difference between the first prediction mode and the reference prediction mode when the first prediction mode and the reference prediction mode are different from each other.   
     
     
         36 . The image encoding apparatus according to  claim 34 , wherein
 the encoded pixel block includes left and upper pixel blocks which are closest to the encoding target pixel block.   
     
     
         37 . The image encoding apparatus according to  claim 34 , wherein
 the second predicting unit is configured to generate a predetermined constant as the reference prediction mode when the reference pixel block and the encoding target pixel block are different from each other in the prediction order.   
     
     
         38 . The image encoding apparatus according to  claim 34 , wherein
 the first selecting unit is configured to select, from  24  prediction orders which are combinations of orders of four sub-blocks obtained by dividing the rectangular encoding target pixel block, a prediction order to the four sub-blocks.   
     
     
         39 . The image encoding apparatus according to  claim 34 , wherein
 the prediction order selecting unit is configured to select a prediction order to four sub-blocks obtained by dividing the rectangular encoding target pixel block from prediction orders: (a) a prediction order given by a lower right pixel block→an upper right pixel block→a lower left pixel block→an upper left pixel block; (b) a prediction order given by a lower right pixel block→a lower left pixel block→an upper right pixel block→an upper left pixel block; and (c) a prediction order given by an upper left pixel block→an upper right pixel block→a lower left pixel block→a lower right pixel block.   
     
     
         40 . An image decoding method comprising:
 decoding encoded data to generate a prediction residual error signal, information representing a selected prediction order, and mode information representing a first prediction mode for each of a plurality of pixel blocks obtained by dividing a frame of an image signal;   selecting a prediction order to a plurality of sub-blocks obtained by dividing a decoding target pixel block from a plurality of predetermined prediction orders;   selecting one prediction mode set including the first prediction mode and a second prediction mode from a plurality of prediction mode sets predetermined to correspond to the plurality of prediction orders and including a plurality of prediction modes having different prediction directions according to the selected prediction order;   predicting the decoding target pixel blocks in units of the sub-blocks according to the first prediction mode represented by the decoded mode information to generate a plurality of prediction signals corresponding to the decoding target pixel blocks;   setting a weighting factor to the first prediction signal depending on the prediction directions of the plurality of prediction modes and a spatial distance between a prediction pixel in the decoding target pixel block and a reference pixel;   calculating a weighted average of the plurality of second prediction signals according to the weighting factor to generate one second prediction signal corresponding to the decoding target pixel block; and   generating a decoding image signal by using the second prediction signal and the prediction residual error signal.   
     
     
         41 . An image decoding apparatus comprising:
 a decoding unit configured to decode encoded data to generate a prediction residual error signal, information representing a selected prediction order, and mode information representing a first prediction mode for each of a plurality of pixel blocks obtained by dividing a frame of an image signal;   a first selecting unit configured to select a prediction order to a plurality of sub-blocks obtained by dividing a decoding target pixel block from a plurality of predetermined prediction orders;   a second selecting unit configured to select one prediction mode set including the first prediction mode and a second prediction mode from a plurality of prediction mode sets predetermined to correspond to the plurality of prediction orders and including a plurality of prediction modes having different prediction directions according to the selected prediction order;   a predicting unit configured to predict the decoding target pixel blocks in units of the sub-blocks according to the first prediction mode represented by the decoded mode information to generate a plurality of prediction signals corresponding to the decoding target pixel blocks;   a setting unit configured to set a weighting factor to the first prediction signal depending on the prediction directions of the plurality of prediction modes and a spatial distance between a prediction pixel in the decoding target pixel block and a reference pixel;   a weighted average unit configured to calculate a weighted average of the plurality of first prediction signals according to the weighting factor to generate one second prediction signal corresponding to the decoding target pixel block; and   a generating unit configured to generate a decoding image signal by using the second prediction signal and the prediction residual error signal.   
     
     
         42 . The image decoding apparatus according to  claim 41 , wherein
 the mode information includes a flag representing whether the first prediction mode and the reference prediction mode are matched with each other and further includes a difference between the first prediction mode and the reference prediction mode when the first prediction mode and the reference prediction mode are different from each other.   
     
     
         43 . The image decoding apparatus according to  claim 41 , wherein
 the decoded pixel block includes left and upper pixel blocks which are closest to the decoding target pixel block.   
     
     
         44 . The image decoding apparatus according to  claim 41 , wherein
 the first selecting unit is configured to select, from  24  prediction orders which are combinations of orders of four sub-blocks obtained by dividing the rectangular decoding target pixel block, a prediction order to the four sub-blocks.   
     
     
         45 . The image decoding apparatus according to  claim 41 , wherein
 the first selecting unit selects a prediction order to four sub-blocks obtained by dividing the rectangular encoding target block from prediction orders: (a) a prediction order given by a lower right pixel block→an upper right pixel block→a lower left pixel block→an upper left pixel block; (b) a prediction order given by a lower right pixel block→a lower left pixel block→an upper right pixel block→an upper left pixel block; and (c) a prediction order given by an upper left pixel block→an upper right pixel block→a lower left pixel block→a lower right pixel block.